Yeah if you have thick layer it could drastically reduce the temperature where the snakes hide is. I ended up just switching to newspaper instead for my rack because I had to turn the thermostat up so high to get the heat to penetrate just a 1/2 inch of aspen. If you want to use substrate just use a little bit to basically just cover the surface. If you turn your thermostat up to high so the heat reaches the snakes hide and your snake burrows down to the bottom of the tub there's a good chance you will burn your snake.